Electronic circuits for controlling illumination intensity in ionizable gas display tubes or the like



Aug. 12, 1958 D D. HANSEN TUBES OR THE LIKE Filed April 19. 1954 FIG. I

5 Sheets-Sheet 1 Sec. l-C

Station Amplifie rUniT 26 25 24 A MosTerlOonTrolunir o i IZM Seal-8'DAYNE D. HANSEN, Sec. Inventor Attorney g- 12, 1953 D. D. HANSEN 2,84

ELECTRONIC CIRCUITS FOR CONTROLLING ILLUMINATION INTENSITY IN IONIZABLEGAS DISPLAY I TUBES OR THE LIKE Filed April 19. 1954 5 Sheets-Sheet 2 Iw Th raTron PIaIe CIrcuII Cu rvenI' How. 0 5 IO I5 H6 2 Time (Seconds)SI N E 50 50 Grid 5305 on c ThgraIron Tube \1 '0 5' no I5 FIG 3 I E mGrid B'Ias of me OuTpuI' of I41 FIG 4 53 53 1-, W PIare CurrenI FIowTube I8 0 5 I0 I5 I FIG 5 54 5s 54 53 54- 53 E VoITaqe Across lCapac'flor 23 o 5 I0 l5 FIG 6 Grid Bias To "STaIIon UnII D YN NSEN LIghTOuIpuT of E Eag Neon Tubes B 15 of W AIIm-ney g- 12, 1953 D. D. HANSEN2,847,616

ELECTRONIC CIRCUITS FOR CONTROLLING ILLUMINATION INTENSITY IN IONIZABLEGAS DISPLAY TUBES OR THE LIKE Filed April 19, 1954 Sheets-Sheet 3 FIG. 9I W Muster Control Umt Sec.9-D

/25a 49a -fl a zoa g W 34 i 18 S 9 x 5 D g B a? 38 2m l. FIGJZ 7 I IO WW?! H" DAYNE D. HANSEN, Inventor L g Sec.9 A BY 4 A v o m I j no vAttorney Aug. 12, 1958 D N ELECTRONIC CIRCUITS FOR CONTROLLINGILLUMINATION INTENSITY IN IONIZABLE GAS DISPLAY Filed April 19, 1954 REDTUBE TUBES OR THE LIKE 5 Sheets-Sheet 4 DAYNE D. HANSEN mvenTor BYAttorney United States Patent ELECTRONIC CIRCUITS FOR CONTROLLING.

ILLUMINATION INTENSITY IN IONIZABLE- GAS DISPLAY TUBES 0R THE LIKE DaynaD. Hansen, Seattle, Wash.

Application April 19, 1954, Serial No. 424,990

17 Claims. (Cl. 315-481) My invention and discovery relates to gaseous.tube display lighting and the production and automatic control ofvarying brilliance of said display lighting, and more particularly to anall electronic control circuit so employed, the same being capable ofoperating: without power driven or mechanically moving parts, such asmotors or solenoids.

In general, it is a primary and fundamental object of my invention toprovide a circuit, that may be employed in any electric circuitin whichan automatically varied or variable current or potential. is. desired toelectronically control such. circuit without employing motor driven ormechanically moving parts.

Also, be it noted, my invention and discovery may be applied toproducing a wave of desired form in producing correlated effects inexperimentation.

This application is a continuation-in-part. of; my ap: plication, SerialNumber 364,415, filed June. 26, 1953, entitled Non-Mechanical and WhollyElectronic Controlled Circuit, which application was copending here withand has been abandoned in favor of the. present application. 1

While my invention and discovery is set forth for purpose of clearnessof description and. illustration in connection with sign lighting, thescope thereof; is not to be so limited but is coextensive where like.problems or conditions exist in whole or in part.

Also, more particularly my invention and discovery relate to theproduction and control of the brilliance, especially of a gaseous tubesign, by providing a master voltage control circuit which controls themagnitude of current of an amplifying means and this in turn controlsthe current of the sign and therefore its brilliance, while at the sametime providing voltage ofv a substantially constant value at all timesof. such magnitude asmay. be required to maintain ionization of suchgaseous medium in the sign-all this without employing mechanicallymoving parts either for the production of such varying brilliance or forthe control thereof. By the terms gaseous and gaseous medium itisto beunderstood there are to be included for example, neon, argon, andmercury vapor which are cited by vway of. illustration and notlimitation.

A primary object of this invention and.discovery is. to provideelectronic means for varying. brilliance. of a gaseous electric signwhereby a gradual dimming of the light emanating from such gaseoustubesign may beaccomplished, followed by a gradual return of the lightttoits normal brilliance, and soon alternating in predetermined timedcycle.

A further primary object of the. inventionis, inthe fields of bothoutdoor and indoor gaseous, tubeillumination, to eliminate the expensiveand'bulkycontrol equip- Pent heretofore employed. In outdoor signillumina- "P particularly, installation space is limited and'often M uof access. The equipment, moreover, cannot concealed as readily as whenindoors. gjm ther primary object is. to avoidthe presenhgem 2,847,616Patented Aug. 12, 1958 2 erally adoptedpractice of custom building of.the control equipment, that. is, specially and. individually. buildingequipment for each particular: signinstallation.

My invention involves (a) a Master Control Unit" and (b) a StationAmplifier Unit; In myinvention, in. contrast with. such specially andindividually custom built equipment, I provide. a Master Control Unitwhich can be constructed of like parts throughout,.i. e., standardized,for all magnitudes of currentjbeing controlled inthe. Station AmplifierUnit. or. in a. number of such. Station Unit Amplifiers. Also the partsof the. Station Amplifier Unit of my inventionv may be. constructedvalike and interchangeable, i. e.,.standardized, withsthe; exceptionofthe amplifying vacuumtriode: Thistubeiis selected. according todifferent rangesof. magnitude of. current. required. For example, one.size of said tubefwill accommodate magnitudes of. current ranging fromone milliampere to 60 milliamperes as is:employ.ed. inucomm'on practice;Another sizeof: such tubeis employedxwherel the magnitude of current'isin thelrange ofj60 milliamperes to 500;milliamperes. Obviously, a tubeoftasize'for SOOtmilliamperes will accommodate a current of from 1.milliamp'ere to 500 milliamperes, but this would b.e.:uneconomical=whensogreatly in excess of the range: sufficient to operate a given sign; Asa. matter of'practice, the current of neon tubes forsign.installationfalligenerally in the ranges-of l to 60.. milliarnperesand 60 milliamperes to 500? milliamperes. For: eighty to; ninety percent(80% to 90%) of thesign tube'installations, the current ratings. offtheneon. tubes fall'in the range of l to 60.n1illiamperes. Thisinterchangeability; and: versatility. of the device: of

. my invention provides. for great economy in: the sign installation andmaintenance.

It is particularly'a primaryobject of my inventiontand discovery toprovide'a completely electronicusystem which employs no motor or.mechanically moving parts, to achieve all of the lighting effects hereinset forth. To.- ward. this objective, itJWill beseen that the inventionproduces a. whole'new series of effects, including wide variation inspeed: of change of brilliance, period of maximum brilliance: andidirnness, and smoothness of blending of lights of different colors inthe field of electrical advertising: and decorative lighting;

It.is also a primary and fundamental object of very great importanceiofmy invention totprovideua neonsign of marked :and especially greateconomyvin manufacture, and, above all, of. especially great economy ininstallation and maintenance the device of myinvention' beingcharacterized by its eflicicncy in operation, eliminating the.consumption of. current by auxiliary motors by: direct consumption andby heat dissipation by resistors.

Afurther primary object ofmy invention is to provide a neon sign whosebrilliance may belchanged gradually either, automatically or manually.

A further and fundamental primary. object of my inventionisto-provide:for changes of color in timed cycles and for. theprecise';synchronization ofsuccessive changes of color by different gaseous tubesin a giveninstallation:

Other objects of anduses. to which. the invention: may be directed-Willbe readilyapparent to those skilled in the art as the descriptionproceeds. For example (by way of. illustration and. not-of limitation.)may benamed the following: The invention can. be used toicontrol airfield. tower markers to :prevent airplane pilots' from losing distanceperspective. Also in experimental work, further,,the control provided.by the invention can be employed in generating signals of low frequencyofanydesired wave formas respects voltage or currentcmagnitudes.Further, the invention is adaptedato operate 35111651301111- dary markerfor airplane fields or runways; The speed of the ;lighting up of thearunway is adaptableito adjustment 3 so as to function as a basis ofcomparison for the pilot in judging his landing speed, or other aid.

The invention and discovery is well adapted for testing devices whichare subject to vibration; by Way of illustration and not limitation,among such applications may be cited the following: In testingvibrations of airplane wings, the device or invention would be useful inrendering uniform and definitely controlled the force producing the lowfrequency vibration of the wings; in short, the invention and discoveryis useful in controlling and rendering uniform the force for developingfrequency of vibration of selected frequency and magnitude, whether ofuniform or unequal magnitude and with either gradual or abrupt changesin said forces.

Tubes employed in advertising, which are filled with an ionizable gassuch as mercury or neon vapor, have the same voltage-currentcharacteristics as any gaseous discharge tube, in that if the voltage ishigh enough it will ionize the gas in the tube and when a certainminimum of current is provided light will be given off. The ionized gaswill then conduct electricity as in the case of any metallic conductoras long as the circuit is maintained. In anygaseous discharge tube, thevoltage must remain above a certain minimum value to overcome resistancein order to keep the gas ionized, but the intensity and brilliance ofthe light given off is dependent upon the amount of current flowingrather than upon the amount of the voltage. Hence, in order to vary aneon tube light over a wide range of light intensities, it is necessaryto be able to vary the flow of current while maintaining an almostconstant voltage, i. e. sufiicient to overcome the resistance, i. e.provide for continued gas ionization. In installations where resultsother than those involving the illumination effects mentioned above, thecurrent may be kept substantially constant and the voltage may bevaried. Such results (by way of illustration and not of limitation)might be the production for study of desired voltage wave forms, inwhich study there would be involved characteristics of tubes and valuesof resistors and condensers.

Devices of the prior art, for varying illumination intensity, have beenapplied to neon gas tubes but have usually failed because they wereunable to maintain a constant voltage with variation in the amount ofcurrent employed. When they did not fail in this requirement, they wereaccompanied with serious disadvantages. As an example, in one existingcontrol system the length of neon tubing ordinarily carried as full loadfor a transformer is reduced to a third or a half of such full loadlength-thus tripling or doubling the cost. Also heretofore, when adecrease of voltage has occurred, the tube has failed completely to giveoff light, due to the de-ionization of the gas, and for many years, thiseffect has been avoided by employing a flasher, i. e., a device operatedby a separate motor, thus involving mechanically moving parts which canonly turn the sign or portions thereof off and on, as distinguished fromvariation in degree of brilliance.

A primary object of my invention is to provide economy of controlinvolved in all the above features as well as others.

Some devices of the prior art, where mercury vapor is involved, to alimited extent have accomplished changes in light intensity bydecreasing the footage of the tubes allotted to each transformer byabout fifty percent. However, this decrease in footage is impracticalfor economic reasons. Furthermore, there is apt to be a constant flickerin the gas-filled tubes when the intensity of light decreases byemploying the devices and methods of the prior art, as for illustration,motor driven auto transformers.

Known methods and equipment for dimming neon and mercury gas-filledtubes for the most part have not been satisfactory because the equipmentneeded for the desired effect requires a great deal of installationspace and also relatively great weight, sometimes several hundredpounds, making it generally impractical for use in sign work since forone reason, said equipment must be hidden and often located in elevatedand relatively inaccessible positions.

Moreover, such prior methods of sign brilliance control equipmentinvolve motor and mechanically moving parts and even with all such theydo not operate to provide a substantial constant voltage. Let it benoted that a driven choke type of means for altering the current isinherently a voltage dropping device and therefore does not provide aconstant voltage while, moreover, involving a decrease in tubingfootage. Such footage must be near maximum to meet optimum economicconsiderations. However, such motorized and mechanical moving means mustbe special, that is, custom made, for each particular installation andare relatively much more complex than the invention herein set forth.Furthermore, all such choke means must operate upon alternating currentonly, while, in definite contrast, the device of my invention is capableof controlling either an alternating or direct current supply and meetsoptimum economical considerations.

The maintenance of the systems of the prior art is expensive, since eachinstallation must be custom-built due to the fact that very seldom dotwo sign installations require the same amount of electrical energyconsump tion; that is, each sign installation involves a diiferentlength of tubing and therefore draws a different amount of power, and tocontrol by motor driven means this amount of power for the particularinstallation, obviously requires the building of control means ofspecial rating for the particular installation. Hence, it follows thateach piece of control equipment would be of a diiferent size or ratingand the parts would not be interchangeable. Experience dictates that itis desirable to have versatility in the desired lighting effect since notwo installations have the same locations and surroundings to make anyone lighting eflect pleasing. In short, different locations andsurroundings dictate different installations to render the sign readableand of pleasing and desired attractive effect, as for example, the speedof change and degree of brilliance. Current, voltage, speed of cycling,and other factors should all be variable for best results, but with thesystems of the prior art these effects cannot be readily, efliciently oreconomically accomplished. In the case of my invention and discovery,all such factors may be varied by a simple adjustment as by turning adial and therefore interchangeableness and versatility are provided, andcustom construction of the control units eliminated.

According to the present invention, the system comprises two basicunitsa Master Control Unit, and a Station Amplifier Unit. One suchStation Amplifier Unit is employed for every so many feet of neon ormercury gas-filled tubing, but such unit can be built beforehand andapplied in any lighting installation regardless of the size or effectdesired, since in the device embodying my invention-the Master ControlUnit is of a construction which is characterized by being able tocontrol all such variations in the Station or Amplifier Unit by a simpleadjustment or presetting of the resistors in connection with thecapacity of the condenser in said Master Control Unit. I have discovereda new, so far as I know, Master Control Unit which may be employed tocontinuously and automatically produce and control the desired varyingbrilliance of the sign regardless of the number of said station unitsemployed-said station units all being of like parts and construction forany given range of magnitude of current, i. e., only the vacuum triodetube rating need by preselected as hereinabove set forth.

The electronic system of this invention produces no flicker of lightduring the dimming or increasing of the brilliance of the neon sign whenproperly applied and adjusted. Its cost of maintenance is relativelyvery small due to the fact that ,the units can be fabricated before-Station Amplifier Unit. One unit may be interchanged for one in itsrange already installed which has failed by long use. The units of myinvention anddiscovery require very little space, a most importantfactor as it avoids the necessity of providing a new housing; and weighbut a few pounds, as of theorder of seven pounds in contrast to fifty toone hundred pounds for mechanically driven control devices. The signvoltage is'maintained substantially constant irrespective of range ofcurrent magnitude.

The invention has the further very important advantage that it isevenapplicable to neon sign installations already in use. Due to theversatility of the Master Control Unit, which may be readily adjusted,the effects obtainable relate to all of the important factors of a neonsign operation such as, the overall length of the cycle, the timerequired for the sign to gradually become dim, the length of time itremains dim, the length of time required to return to full brilliance,the length of time it remains at full brilliance and the degree ofbrilliance and degree of dimness.

Briefly summarized, and therefore incompletely set forth, the inventionand discovery involve the following:

The providing of a Master Control Unit of like and interchangeable partswhich function to exert a variable control signal on the grid of one ormore triode tubes in the Station Amplifier Units provided by theinvention, while at the same time providing voltage of a substantiallyconstant magnitude as maybe required to maintain ionization of suchgaseous medium. The function of the invention as a whole; that is, theMaster Control and the Amplifying Units, is to exert an adjustablecontrol upon the current delivered to the neon sign whereby the operatoris enabled to make a setting by simply adjusting a dial which results ina light cycle of brilliance-fadingbrilliance at desired intervals, saidfactors being more fully set forth herein.

The disclosure of my invention relates in general to two forms, one, avery simple form as illustrated in Figure 1 herein, and the other, amore complicated form of my invention which is particularly adapted toeffect a gradual change and blending of colors in the lighting systemwhich has some of the tubes provided with mercury vapor and some withneon gas, as illustrated in Fig. 10.

The above mentionedgeneral objects of my invention, together with othersinherent in the same, are attained by the mechanism illustrated in thefollowing drawings, the same beingpreferred exemplary forms ofembodiment of my invention, throughout which drawings like referencenumerals indicate like parts:

Figure l is a diagram of a simplified form of electric circuit embodyingmy invention and discovery particularly adapted for varying thebrilliance of the light emanating from the sign in -an automatic timedcycle;

Fig. 2 is a representation of the normal current wave form with respectto time which characterizes the normal operation of the thyratron platecircuit, i. e., a circuit which is either conducting or non-conducting;

Fig. 3 is a representation of the wave form of the signal voltageimpressed upon the thyratron tube grid;

Fig. 4 is a representation of the output voltage signal wave form withrespect to time at the output of sec. 1-A;

Fig. 5 is a representation of the plate current flow of the vacuumtriode tube with respect to time in sec. lB;

Fig. p is a representation of the voltage wave form with respect to timeof the combinedtor final wave form produced by sec. l-A and sec. 1 Batthe output of sec. 1-B;

Fig. 7 is another or separate representation of thecombined or finalform of wave as received 'by the Station Amplifier Unit; i. e. it is aportion ofthe alternating (A.-C.) component of output of sec. l-B, fromwhich a portion of the direct current (D.-C.) component .has beenremoved;

Fig. 8 is a representation of the light output of the neon tube of thesign, thereby indicating the brilliance and dimming cycle;

Fig. 9 is a diagrammatic illustration of a modified electric circuitcomprising a Master Control Unit and a Station Amplifier Unit accordingto my invention and discovery, especially adapted for use with othersimilar units in a sign having a plurality of gaseous tubes, each of adifferent color or effect, which plurality of tubes is to be operated insynchronization successively, but also adapted to produce the result oroperation of the circuit of Fig. 1, only one such .circuit and one suchgaseous tube being shown;

Fig. 10 is a diagrammatic illustration of the electric circuit embodyingin united and connected representation a plurality of the units setforth and illustrated in Fig. 9 where the same are connected forsuccessive and synchronized operation of colored tubes;

Fig. 11 is a diagrammatic illustration of an electric circuit of myinvention illustrating a modified form of sec. 1-A of Fig. l;

Fig. 12 is a diagrammatic illustration of a modified form of the StationAmplifier Unit employingan impedance element;

Fig. 13 is a view of Fig. l with the valves of the elements set forth inthe drawings; and

Fig. 14 is a view of Fig. 11 with the valves of the elements set forthin the drawings.

In Figure 1, for purposes of description the Master Control Unit whichmay be otherwise termed a lowfrequency control signal generator, hasbeen separated into two sections, sec. 1-A and sec. 1-B, by .the dottedline B-B. Also the Master Control Unit as a whole has been separatedbythe dotted line A-A from the Station Amplifier Unit, sec. 1C sodesignated.

Master Control Unit Referring to see. 1A thereof, a transformer 11delivers alternating current power from the source lines 10, and thenceto a rectifier 12 when main switch 12M is closed. Parenthetically, letit be noted 3 that here the description hereinafter set forth willproceed in the direction of the electron flow, as contrastedtothedirection of positive current flow, to provide clear and fulldisclosure. The rectifier 12 may be of any type, but that shown is afull-wave vacuum tube type in combination with a center tap typetransformer 11, which is considered the preferred and most practicaltype. transformer for this use. Electron flow starts from the center tapof transformer 11, thence through impedance 49, adjustable variableresistor13, through and charging the condenser 14, thence from resistor13 and condenser '14 through the variable resistor 15 and condenser 16to the cathode of tube 17. Tube 17 is a gaseous type gridcontrolledrectifier tube, known as a thyratron, and is supplied with power fromtransformer 11 and rectifier 12.

Thus an alternating current as a source of electrical energy inconductors 10 is connected to a transformer 11 and the plate of arectifying tube 12 to produce a pulsating source of direct current. Ofcourse an equivalent of this would be any of the several well knownmeans for producing a pulsating direct current. From the plate of tube17, electrons flow back to the rectifier tube 12, to complete the directcurrent (D. C.) circuit. Impedance 49 functions to limit the peakcurrent flow through the thyratron plate circuit and also to providegreater variety charged. The grid of tube 17 is connected to condensers14 and 16. Hence, when condenser 16 becomes charged, the potential onthe grid of tube 17 is negatively high. This high negative gridpotential results in a sudden extinguishing of the flow of currentthrough tube 17. Condensers 14 and 16 primarily discharge gradually, anadjustable time constant being provided by variable bleeder resistors 13and 15. Since the negative voitage drops as the condensers 14 and 16discharge, the negative potential on the grid of tube 17 must drop also.When such bias is low enough, the cut-off point of tube 17 is exceeded,and the current will again flow, as described above. Thus, sec. 1-A ofthe Master Control Unit of Figure l is what may be termed a free-runningrelaxation oscillator.

As set forth above, the negative bias on the grid of tube 17 is for thepurpose of momentarily interrupting, that is, shutting 011 the currentfiow through gaseous tube 17. This interruption of current has theeffect of automatically and inherently interrupting the current supplyto resistor 13 and condenser 14. Such interruption allows the condenser14 to discharge at a rate depending upon the capacitance thereof and theimpedance value of resistor 13. All such operation of charging the saidcondensers 14 and 16 and controlling their discharge through saidresistors 13 and 15 is for the express purpose of generating a wave formof voltage which is illustrated in Fig. 3.

More explicitly, when the switch 12M is closed, the current momentarilyflows across condenser 16 and through tube 17. Such flow is onlymomentarily at the time of closing said switch. In the next interval oftime, the current commences flowing through resistor 15, imposing anegative bias, i. e., voltage on the grid of tube 17 which, as statedabove, definitely shuts off the current flow through tube 17. Thecircuit shown in sec. l-A, including transformer 11, resistor 13,condenser 14, condenser 16, resistor 15, tube 17, and rectifier 12creates as its output a wave form as shown in Fig. 4. In the presentdisclosure, resistor 15 may be of relatively high or low impedance valuein comparison to resistor 13 depending upon the output wave formdesired. The sudden flow of the electric current through tube 17provides a voltage represented by the vertical components 50 (Fig. 3).Thereupon resistor 15 imposes a gradual discharge of the voltage and isrepresented by the curve 51.

In a device already built embracing this invention, the above cycle orrepetition rate is variable within the following limits: From one cyclea second to one cycle per twenty minutes, and as a practical matter,this is the range required. However, inherent characteristics of theinvention permit a much wider range. The length of the cycle depends onthe resistance and adjustment of bleeder resistor 13 and resistor 15which discharges condensers 14 and 16 and on the capacitance ofcondensers 14 and 16.

The second section of the master control unit, sec. l B, lying betweendotted lines A-A and B-B, is the same in general arrangement as thefirst section 1A, and current flow is basically the same, with but twoexceptions. Gaseous tube 17 is replaced by tube 18, a pliotron, which isa vacuum or hard. Hence, tube 17, (a gaseous triode) which has thefunction in sec. 1-A of allowing a current to be on or off, has beenreplaced by tube 18 (a vacuum triode) which has the function in sec. 1-Bof affording a predetermined varying control over the amount of thecurrent flowing through tube 18. Resistor 15 and condenser 16 arereplaced by a potentiometer 19 across the terminals of condenser 14 ofthe first section lA. This potentiometer 19 provides a control signalbetween the cathode and grid of tube 18, thus connecting the circuits ofsec. lA and sec. l-B.

The electron flow in sec. l-B may be traced as follows: Electrons leavethe center tap of the transformer 24 and flow through the impedance 49M,the variable, i. e., predetermined adjusted resistor 22, charging thecondenser 23, thence flowing through triode tube 18, through rectifiertube 21, and thence to transformer 20, to complete the circuit.Impedance 49M functions to limit the peak current flow through thevacuum triode plate circuit. However, impedance 49M may be omitted whennot required or desired. Rectifier 21 may be any type of rectifier, afull wave rectifier being presented for illustration.

The electron flow just described occurs only when the negative potentialfrom sec. lA on the grid tube 18 is low enough negatively to permit theelectrons to flow in said circuit. When the negative potential on thegrid of tube 18 becomes too high to permit the electrons to flow throughtube 18, the condenser 23, which has become charged from the line flowof current, begins to leed or discharge through resistor 22, until thenegative grid potential is again low.

As stated above, the function of the pliotron tube 18 is to provide apredetermined adjusted or so called, in practice, a variable controlover the amount of the current flowing through tube 18.

The voltage Wave form of sec. 1-B has superimposed thereon, i. e., ismodified by the wave form of sec. 1A, producing at its output thevoltage wave form shown in Fig. 5, i. e., the wave form of sec. l-A isinverted, in effect, in the wave form of sec. l-B. The final resultingform of simultaneous action of secs. 1-A and l-B produces the form ofwave shown in Fig. 6. In Fig. 7 the wave form of Fig. 6 is separatelyshown and constitutes a basis for comparison with the wave form whichcharacterizes the light output.

Thus, it will be apparent, that the purpose of the Master Control Unit,which may be otherwise termed a lowfrequency control signal generator,is to give a gradual, varying voltage, which if plotted, would appear ingeneral pattern similar to or resembling a sine curve. More accuratelythe curves will be seen as exponential charge and decay curves,according to the predetermined time constants and capacitance of therespective circuits.

The desired control signal for the Station Amplifier Unit isaccomplished by the condensers 14 and 23 and the bleeder resistors 13and 22, which in combination, eliminate the necessity of employing amotor-driven varying potentiometer. It follows that the elimination ofthe potentiometer results in the elimination of maintenance trouble,repair and costs of current or power for the motor.

The exact form of the voltage curve referred to, may be varied inmagnitude and periodicity to produce the desired ultimate effect in thedimming and brightening cycle of the neon gas-filled tubes as aboveexplained.

Station Amplifier Unit Reference is made now to the Station Amplifier orUnit, sec. 1-C, divided from the Master Control Unit by the dotted lineAA for the purpose of illustration. The Station Amplifier Unit iselectrically connected to said Master Control Unit by the leads 25 and26 and the potentiometer 24. The lead 25 is connected to the grid of thetriode tube 34 of the Station Amplifier Unit. The Master Control Unitbiases the grid of tube 34 with a predetermined, automatically varyingcontrol signal, as

desired. The Station Amplifier Unit consists of power were ' leads 30and 31 and four tubes, 35, 36, 37, 38, con- 34, through tube 38 andthence out through lead 31.

On the other half of the cycle, the electrons flow from lead 31, throughtube 35, thence through tube 34 and thence through 37 to lead 30. Theconventional neon or mercury gas-filled tube 32 in the form of a sign orportion of a sign is connected between the leads 30 and 3.1, as shown.Other gas-filled tubes or electrical loads can be. substituted for thesign 32. A transformer 33 is connected as shown to provide the desiredoutput voltage.

Since the grid voltage of tube 34 is controlled by the Master ControlUnit, the flow of electrons between the cathode and plate of tube 34 iscontrolled by the Master Control Unit. Thus, in turn, the flow ofelectrical energy between leads or conductors 30 and 31 is controlled bythe voltage on the grid of tube 34. Thus, the timed cycle of dimming andbrilliance of the sign lighting or output is provided entirelyelectrically and without, be it noted, any mechanical moving parts. i

The resistor 49 throughout the drawings is a current limiting resistor,same being true for 49M, 49N, 49a, 49b and 490.

In the event that the sign represented by tube 32 herein is not of suchlength as to produce an overload, then it would be possible under suchcircumstances to employ the Master Control Unit to operate additionalinstrumentalities by inserting or connecting the same in the conductorleading from tube 34 to 38 or from tube 36 to tube 34.

While the invention has been designed particularly for neon tubebrilliance control, it is, nevertheless, obvious that it could beemployed in any circuit in which an automatically varied or variablecurrent or potential is desired to be electronically controlled withoutemploying mechanically moving parts since, with the arrangement shown,the operator can change the form of the wave representing the voltage byproper setting of the resistors and preselection of the other circuitcomponents to produce various periodic cycles and forms of curves. Forexample, by adjusting the impedance value of resistor 15, the over-alllength of time for the cycle period is determined; by adjusting theimpedance value of resistor 13, the length of time required for dimmingthe sign. Of course, it would be understood that increasing theimpedance value of the resistors will increase the period or the curvecomponent of the wave both in dimming and in increasing the brilliancy.In further adjusting the circuit time constants, the potentiometers 19and 24 must be considered. By selecting a particular setting of the saidpotentiometers the degree of sharpness of the curves can be altered;that is, they can be softened, rounded or rendered more smooth and thechange in the brilliancy of the sign would not be so abrupt. The maximumbrilliancy and the maximum dimness can be controlled by the setting ofthe potentiometer 24. If the resistance setting of potentiometer 24between leads 25 and 26 is increased, then the brilliance in the neontube will be decreased and vice versa.

As illustrated, an alternating current as a source of electrical energyin conductors is connected to a transformer 11 and the plate of arectifying tube 12 to produce a pulsating source of direct current. Ofcourse, an equivalent of this would be any means for producing apulsating direct current.

The source of energy for sec. l-B that is the modifier unit for saidhalf cycle may be derived from the alternating current of conductors 10with transformer 20 and rectifier tube 21. As an equivalent any sourceof direct current may be employed so that the transformer 20 and Sincethe invention is designed to function 10 rectifier tube 21 maynot benecessary. This direct cur rent need not be a pulsating current. Infact, while it will work with pulsating direct current, it is preferablenot to use a pulsating current if a filtered direct current source iselsewhere available.

Another procedure of following the current is as follows, same being setforth for clearness of description: The direction of positive currentflow is as follows: in section l-A, transformer 11 delivers current tothe plates of full wave rectifier tube 12 and from the cathode of tube12 to the plate of thyratron tube 17. From the cathode of tube 17 thecurrent flows through the capacitor 16, variable resistor 15 combinationto the parallel combination of capacitor 14, variable resistor 13 andpotentiometer 19. Out of this parallel combination the current flowsback to the center tap of the secondary of transformer 11 to completethe D.-.C. circuit. Note conductor 15x connected to the grid of thethyratron tube 17, which at certain times will supply negative bias tothe grid of tube 17, and thus make possible the interruption, ofcurrentfiow in the plate circuit of the thyratron. The D.-C. supply is leftunfiltered to provide short deionization periods of the gas in thethyratron tube so that the thyratron grid may at certain times gaincontrol of the thyratron plate current.

The function of variable resistor 15 is to create the negative bias onthe grid element of the thyratron tube 17. The function of capacitor 16shunted-around resistor 15 is to allow an initial instantaneous flow ofplate current in the thyratron for the purpose, as will be eX- plainedlater, of charging capacitor 14 before the current flow through resistor15 can cause a negative bias on the grid of the thyratron which will cutoil the flow of thyratron plate current. The high negative bias on thethyratron grid is caused by the thyratron plate currentflowing throughthe cathode resistor 15. In other words, plate current flow producesnegative grid bias, the grid bias stops the fiow of current whichcreated the bias and at the instant that current flow stops, the gridbias gradually decreases to zero and allows plate current to again flowin the thyratron. The gradual decrease of grid bias is obtained asfollows: capacitor 16 has become charged during this instant of currentflow, the charged capacitor supplies the negative grid bias to thethyratron :after plate current flow ceases and thus keeps plate currentfrom flowing for the period of time required for the capacitor voltageto decay to almost zero. The time required for the capacitor voltage todrop is determined by the RC time constant of resistor 15 and capacitor16. When this gradually decreasing grid voltage reaches a certain lowvalue, it no longer stops the flow of plate current and plate currentwill again flow for an instant, that is, just long enough to rechargecapacitor 16 At this time the grid bias becomes high and again stops theplate current flow until such time that the voltage of capacitor 16decreased, due to bleeder resistance 15, to a value low enough to allowthe flow of plate current to start the next cycle. Variable resistor 15serves two purposes, first, as the cathode resistor to supply negativevoltage to the grid of the thyratron while plate current is flowing ineach cycle and, second, it serves as the bleeder resistor for capacitor16 during the rest of the cycle. Since the. resistance of resistor 15determines the length of time required for the voltage of capacitor 16to decrease to a low value, it therefore, determines the frequency ofthe cycle.

Resistor 15 is a variable resistor which makes it possible to select thedesired frequency.

The wave form of the thyratron tube 17 plate current is shown in Fig. 2by vertical line 50. The wave form of voltage impressed upon the grid ofthyratron tube 17 byresistor 15 and capacitor 16 is shown in Fig. 3 bylines 50 and 51.

It should be noted, that the initial surge of thyratron plate currentwhich marks the beginning of each cycle, Fig. 2, cannot take place untilthe negative grid bias supplied by capacitor 16, shown as curve 51 ofFig. 3, has gradually decreased to a value so low that it can no longerstop the flow of thyratron plate current.

The RC time constant of capacitor 14 variable resistor 13, also includedin section l-A of Figure 1, need not have the same RC time constant ascapacitor 16 resistor 15 combination which determines the frequency. Oneof the voltage wave forms obtainable across the terminals of capacitor14 is shown in Fig. 4 by lines 52 and 52M, that is, for any one selectedfrequency.

Potentiometer 19 connected across capacitor 14 of section 1A in Figure 1supplies negative bias to the grid of vacuum triode tube 18 in section1-B. Section l-B is basically an amplifier circuit which will be usednot as an amplifier but as a means of inverting the voltage waveproduced across the terminals of capacitor 14 in section l-A. One of themany possible inverted waves is shown in Fig. by lines 53 and 53M. Asstated above, section l-B inverts the voltage wave of section 1A and inaddition, section 1-B produces a component of the voltage wave of itsown which it adds to the inverted wave. The added component of voltagewave is shown as curve 54 in Fig. 6. The resulting voltage wave is thefinal signal voltage that is sent to the Station Amplifier Unit in eachneon tube circuit to control the light output.

It is possible for section 1-B to produce its own component of voltagewave form and add it to the inverted wave because of the parallelcombination consisting of variable resistor 22, capacitor 23 andpotentiometer 24, which is connected as the load on amplifier circuitsection lB. The gradually increasing current flow in section lB which ina sense is the inverted wave of section 1A, Figs. 5 and 6 curve 53,gradually increases the voltage drop across resistor 22 which in turnincreases the voltage impressed upon capacitor 23. The voltage acrosscapacitor 23 will rise to its maximum value at a desired rate and willremain at this maximum voltage until such time that thyratron tube 17starts a new cycle, i. e., is cut off. When the new cycle starts, thecurrent flow in section l-B is instantly cut off but the voltage acrosscapacitor 23 will decay at a rate determined by its RC time constant.Thus, the component of voltage wave form shown in Fig. 6 as curve 54 isproduced.

The portion of the final voltage wave form produced by section l-B isforced to have the same frequency as the inverted voltage wavecontrolled from section l-A, but the wave form of the added component,curve 54 in Fig. 6, produced by section 1-B need not be symmetrical withthe inverted wave form curve 53, Fig. 6.

Curves 53 and 54 can each be varied from an almost vertical position toan almost horizontal position by means of variable resistors 13 and 22,respectively, assuming the time dimension constant. Variable resistor 15independently controls the control cycle frequency. Potentiometer 24controls the maximum value of signal voltage to the Station AmplifierUnits, yet to be described, and the potentiometer 19 will vary the shapeof either the top or bottom half of the final voltage wave produced bythe Master Control Unit. Thus, the Master Control Unit produces anextremely low frequency control signal where frequency, all componentsof wave form, and magnitude of voltage may be selected.

Station Amplifier Unit The Station Amplifier Unit circuit diagram isshown as section l-C of Figure 1. It consists of a bridge rectifiercircuit using half wave rectifier tubes 35, 36, 37 and 38. A vacuumtriode tube 34 is connected across the D.-C. portion of the bridgerectifier as shown. The alternating current flowing in the neon tubes isrectified so that both halves of the 60 cycle A.-C. flow as rectifiedunfiltered 111-0. through vacuum triode tube 34.

The low-frequency control signal produced by the Master Control Unit isimpressed upon the grid of the vacuum triode 34 by means of conductors25 and 26.v This grid bias controls the unfiltered direct current flow--ing in the plate circuit of the vacuum tube 34 and, therefore, controlsthe flow of 60 cycle alternating current in the neon tubes. The 60 cyclealternating neon tube current wave is a reproduction of the voltage waveproduced by the Master Control Unit.

Since the brilliance of a neon tube is a direct function of current, thelight output of neon tubes will vary auto matically in a cycle ofbrilliance, fading and then gradual returning to full brilliance in atimed cycle as determined by the control signal from the Master ControlUnit.

In the modification shown in Fig. 9 there is shown diagrammatically anelectronic arrangement similar to the circuit of Fig. l and alsosuitable for automatically generating a varying voltage in the MasterControl Unit and controlling either voltage or current in the StationAmplifier Unit.

Parts of the circuits of Fig. 9 which are the same as: in Fig. l aregiven the same numbers with the subscript a added thereto forfacilitating the identification of parts.

This modification (i. e. the circuit of Fig. 9 as compared with that ofFig. 1) consists in eliminating some of the parts described and shown inconnection with Fig. l, and replacing those parts with another circuitwhich will produce the same final results as achieved with thearrangement of Fig. 1 but of a character which may be employed in aplurality of circuits for a plurality of tubes to produce desiredsynchronization thereof.

The parts of sec. 1A not appearing in the corresponding circuit portionof Fig. 9, i. e. sec. 9-A are variable resistor 15, condenser 16, andthe conductor 15x connecting these parts with the grid of tube 17.Modification, in terms of reconstruction of the circuit, is begun byconnecting the cathode of the tube 17 to ground 40.

Other parts added, as shown, in Fig. 9, include the potentiometer 41across the output of sec. 9-13 in parallel with potentiometer 24; thesec. 9-D comprising a transformer 42, triode tube 43, and a rectifiertube 44.

In Fig. 1, sec. l-A circuit is capable of operating by itself; that is,it is self starting and then it operates and impresses its operationupon the circuit sec. l-B and the resultant action of lA and lB istransmitted to lC. Relative the circuit of sec. l-A is self starting:This self starting arises by reason of the fact that the resistor 15momentarily operates to hold back the electrons and impose a negativepotential on the grid of the tube 17. However, just before thiscompletes this complete negative operation by implanting the negativepotential on the grid, there is a leaking of electrons through thecondenser 16. At the first instant of each cycle the electrons flowthrough the condenser 16 and through the tube 17. After this firstinstant, the electrons will no longer pass through the condenser 16(since same will have become charged and no longer is there a change ofvoltage as required for a current to pass through a condenser or asoften now called capacitor), but flow through resistor 15, creating anegative bias or voltage on the grid of tube 17. This results from thefollowing: The resistor reduces the electron flow through the resistorthereby building up a potential which-also builds up a potential on thegrid. It is to be particularly noted that there is a connection 15x fromthe resistor to the grid. This conductor makes it possible to buildnegative potential on the grid.

In the embodiment of the invention illustrated in Figure 1, reviewedhere for later comparison with the modification thereof illustrated inFig. 9, the condenser 16 and the resistor 15 render the circuit of sec.1A self starting. Further, in the sec. l-A circuit in Figure l, theelectron flow passes from the transformer 11 to the resistor 13 and thento the condenser 16 during only the first instant of the cycle, and onthrough the tube 17.

:13 Whilethis is occurring, the potential is developed to a point thatit places a negative potential on grid of tube 17, then this issufficient to stop the flow of the electrons to the condenser 16momentarily. Since the electron flow now has been stopped, .thengradually the negative potentialon the grid of tube 17 decreases tovalue so low that it loses its effectiveness and can no longer interrupta structure of a sign for a colored display, we may have one gaseous, asa neon, tube over or laterally adjacent another gaseous tube, as forexample, a mercury tube. Thus, the operation of the tubes successivelymust be sharply synchronized in producing the desired effect, i. e., onemust be definitely terminated and the other must light up immediatelythereafter to provide the proper effect. This synchronization isnecessary in order to provide control of a desired blending effect for amulticolored sign.

The above requirements for synchronization are met by the circuitarrangement set forth in Fig. 9, wherein transformer 42 and rectifiertube 44 supply power to triode tube 43 which operates as an amplifiertube just as the triode tube 18 does in sec. 9-B, which sec. 9B in turndirectly corresponds with sec. 1-B, of Figure 1, previously described.Across "the output of sec. 9-D is a potentiometer 45 which may be termedthe load of circuit of 9-D. The selector contact of the potentiometer 41is connected to the grid of triode tube 43 by a conductor 46. Thepotentiometer 45 has its selector contact connected to the grid ofthyratron tube 17 by a conductor 47.

Sec. 9A is not self starting as is see. 1-A already described above. Inthe case of 9A, it performs its operation, and this is imparted uponsec. 9-B. When it has imparted its operation upon sec. 9B, then sec. 9Acloses and shuts down operation. Sec. 9-B having been startedinoperation, it performs its function in effecting the form of thevoltage wave and it likewise concludes its operation and shuts down.However, it does not do so until it has in turn imparted its operationupon the circuit of sec. 9-D and started 9-D in operation. Then 9Dperforms its function and before it concludes its operation, however, ithas a conductor returning to sec. 9A. This starts sec. 9A over again andthus the cycle ofoperation continues. Hence, this arrangement or circuitprovides for a definite time of starting the circuit of sec. '9--- A anda definite time of startingof the circuit of sec. 9 B and aastarting ofcircuit of sec. 9D, which i. e. 9D may be termed a recycling circuit, aswell as a conclusion of operation of each one of these sections.

The combined operation of sec. 9A, sec. 9-B and sec. 9D is as follows:Sec. 9A controls the operation of sec. 9B; sec. 9B controls theoperations of sec. 9D, and. sec. :9-;-D controls the operation of sec.9A. The

.time. required for the complete cycle to be developed is dependent uponthe total resistance across the output of sec. 9A and sec. 9-B.Resistors 13a and22a in sec. 9A and sec. 9-B, respectively, regulate thetime required to discharge condensers 14a and 23a in sec. 9A and sec.9-B, respectively. A ground 50 is provided in connection with conductor26a in the Station Amplifier Unit, to correspond with ground 40 of thislead in the Master Control Unit.

The above sets forth the definite operation for a one color system ofsign tubing. It provides for the definite 14 starting and concludingofincreasing the brilliance in the single tubingto high brilliance and.then to dinmess.

By employing the modification shown in Fig. 9 .it ;is possible toproduce the same lighting effect ,as .is described in connection withFig. l. Theadvantages, however, are theadded varying effects inelectrical advertising, and the further applications in severalindustrial fields, wherein the Master Control Unit of Fig. .1 could notbe employed since it would not provide the precise cycle repetition ratewhich characterizes the operation of the modified circuit of Fig. 9.

If it is desired to 'have a second colored tube synchronized in itsoperation with the first colored tube, then that would beaccomplished asset forth in themodificationof Fig. 10. In Fig. 10 is a reproduction ofsections 9A, 9 B, 9C and 9-D of Fig. 9. The sections in Fig. 10corresponding to the sectionspresented in Fig. 9 are identified assections 10-,A, 10 B, lO-C and 10- D for one color tu be of themulti-tube system. For a second color tube, there is the reproductionoflike sections, designated as sections 10A 10-3 1().C and l0-D Moreparticularly and in detail in, Fig. 10 is represented .said circuit ofFig.9 employed with other like .unit circuits in a .sign having aplurality of different gaseous tubes, each of a different color oreffect, which plurality of tubes is to be operated sucessively insynchronization.

;In Fig. 10,,circuits of secs. 10A, lO-B, 10-C and 10- D ,are thecircuits for controlling theoperating of one tube, for example, the neonor red tube. The other part of the Fig. 10, namely, the circuits ofsecs. l0-A ,110-'B 10-C and 10-D are the circuits for operating the second colored tube, namely, the mercury or blue tube.

Parts of. the circuitsof Fig. 1 0 are the same as those for the circuitsof Fig. 9 and accordingly said like parts are given the same number withthe subscript. (b) for the neon or red tu-beand the subscript (c) forthe mercury .or blue tube.

Master Control Unit for the blue tube. .60 extends from thepotentiometer 456 of the Control InFig. 10 the conductor 50 extends fromthe potentio meter 45b of the Master Control Unitfor the red tube to thegrid ofthyratron tube .17c of sec. 10-A of the The conductor Unit for.the blue tube to the grid of .thyratron tube 17b ,of sec. lO-A of theMaster Control Unitfor the red tube.

The operation of the corresponding parts ofthe circuits shown in Fig. 9and in Fig. lO are identical in all resQects and accordingly vwillnotberepeated in the interest of brevity.

Since,- as pointed out above, the operation of circuit IO-Ain a given.cycle completes its eration and then ceases to operate, but not untilit has started the operation of the. circuit of l0-B. Circuit of sec.IIO-B in turn completes its operation for the given cycle and ceases tooperate, but not until it has started the operation of the circuit ofsec. 10.,'D. Circuit of secplO-D in turn com- .pletes its operationforthe given cycle and then ceases .to operate, butnot untilit has startedor triggered the v. and 1-0.D. Sec. Ill-D doesnot cease its operationuntil it has started the circuit of sec. 10-A through conductorconnected to the grid of thyratron tube 17b; tl1at.is, the tube in theControl Unitfor the red tube.

Since the operation of the circuit of the said sections all, operate indefinite time sequence, one following the other, provision is. thusmadefor precise cycle repetition rate and synchronization of the dimmingand brilliance of the separately colored tubes.

Fig. 11 is a representation of a modified form of the circuit of sec.1-A of Fig. 1. In this modifiedform, a transformer 70 deliversalternating current power from the source line71 and thence to arectifier 72 when main switch 73 is closed. The rectifier may -be of anytype, but that shown is a full Wave vacuum type in combination with acenter tap type transformer 70 which is considered the preferred andmost practical type for this use. Electron flow starts from the centerof transformer 70, thence through impedance 49N, adjustable variableresistor 74, through and charging the condenser 75, thence from resistor74 and condenser 75 to the cathode of tube 76. Impedance 49N functionsas impedance 49 and like impedance 49, may be omitted. Tube 76 is agaseous type control rectifier tube, known as a thyratron. The tube 76,which is herein supplied with power from transformer 70 and rectifier 72is a gaseous triode operating on a low-pressure gas. From the plate ofthe tube 76, electrons flow back to the rectifier tube 72 to completethe direct current (D. C.) circuit.

The operation of the part of this modified form of circuit follows thesame operation as that set forth in detail for corresponding parts ofthe circuit of sec. l-A of Fig. 1. The operation of sections 1B and 1D;that is, of the other sections, all operate as set forth in detail forthe corresponding section of Fig. 1.

The diiferences betwen the circuit as set forth in sec. l-A of Fig. land the circuit of sec. 11-A of Fig. 11 are as follows: In sec. 1-A,there are two independent control means, one for selection of frequency;that is by means of adjustable resistor 15, and one for selection of thewave form; that is by means of adjustable resistor 13. In the modifiedcircuit of sec. 11-A illustrated in Fig. 11, there is but one controlmeans; namely, adjustable resistor 74, so that when a desired frequencyis selected, then there is automatically selected an inherent wave forthat wave form for that particular frequency.

In choosing a load circuit for purposes of definiteness of illustrationand clearness of disclosure, 2. load circuit of the character requiringa constant voltage has been adopted. It requires a substantiallyconstant voltage to' maintain the ionization of the gas used in thegaseous tube. Accordingly, a tube 34 of a character which would supply aconstant voltage has been adopted as the tube 34 in the amplifyingcircuit. However, in other load circuits, it may be important to havethe current relatively constant and the voltage vary. When such is thesituation, then a vacuum tube diiferent from that used in 34 would beemployed; viz, a vacuum tube having different characteristics-one whichwould give a relatively constant current and permitting a varying of thevoltage. The Master Control Unit would all be the same where the lattersituation is desired, viz, where the current is to be maintainedrelatively constant and the voltage varied.

In Fig. 12, impedance 90 is connected between the cathode and plate ofvacuum triode tube 34; functioning among other purposes to prolong thelife of the tube, to limit the plate voltage of said tube 34, when usedwith neon tubes as a load, to prevent deionization of the gas; i. e.complete extinguishing of the light, and to adapt the circuit to loadsother than lighting. Impedance 91 (with or without impedance 90) may beconnected between electrical conductors 30 and 31 and would function inaddition to those named above for impedance 90 to protect rectifiertubes 35, 36, 37 and 38, together with associated parts of said tubessuch as filaments. Impedance 90 or 91 may be omitted where theirrespective functions are not desired or required.

In Fig. 12, the vacuum triode tube 34 is illustrated as positionedwithin the bridge of the station amplifier unit, i. e. it is connectedin series in the D. C. portion of the bridge rectifier circuit and is inall respects electrically identical to that shown in sec. 1-C of Figure1 and like sections of the other figures.

While for purposes of illustration several forms of this invention havebeen disclosed, other forms thereof will become apparent to thoseskilled in the art upon reference to this disclosure, and, therefore,this inven- 16 tion is to be limited only by the scope of the appendedclaims and prior art, when the same are construed in the light of thedisclosure herein. In short, equivalents are to be deemed includedherein.

My invention and discovery has been constructed and incorporated inspecific embodiments in accordance with the herein specification and asset forth in the drawings Figs. 1-12 inclusive, and such embodimentshave been successfully operated. The elements, tubes and equipment inthese embodiments operating on a timed cycle of the range of one secondto about one minute, i. e. high brilliance to high brilliance, employedcircuit constants or values for the respective elements, capacitors,potentiometers, resistors, transformers and internal pressure of thedischarge lamp loads as follows:

Fig. 1

Transformers 11 and 20 have primary winding 100 volts, secondary 700volts with a center tap.

Tubes 12 and 21 are standard 5Y3 rectifier tubes.

Tube 17 is a standard thyratron tube 2050.

Adjustable resistor 15 is a one megohm potentiometer.

Condenser 16 is a one microfarad condenser, 400 volts.

Adjustable resistors 13 and 22 are each 3 megohm standard volumecontrols.

Potentiometers 19 and 24 are standard 10 megohm potentiometers.

Condensers 14 and 23 are each 2 microfarad condensers, 400 volts.

Resistors 49 and 49M are each 500 ohm carbon resistors.

Tube 34 is a 211 standard transmitter triode.

Tubes 35, 36, 37, and 38 are standard 816 half Wave mercury rectifiers.

Neon tube 32 may be any gaseous discharge tube of inside diameter of 20mm. and with a gas pressure ranging from about 0.5 millimeter of mercuryto about 20 millimeters of mercury.

Transformer 33 is any ordinary neon tube transformer-the one used herehas a primary voltage of 110 volts, 60 cycles, and a secondary voltageof 2500 volts.

All electrical conductors 15X, 25, 26, 30, 31 and all of the conductorsconnecting in element sections l-A and 1-B are of ordinary number 14gauge insulated wire insulated for 400 volts.

Tube 18 is a 6P5 standard vacuum triode.

Figs. 9 to 12 Transformers 11a, 20a and 42 have primary windings volts,60 cycle, and secondary winding 700 volts with a secondary center tap.

Tubes 12a, 21a and 44 are standard 5Y3 full wave rectifier tubes.

Tube 17a is a 2050 standard thyratron tube.

Adjustable resistors 13a, 22a are standard 3 megohm potentiometers.

Condensers 14a and 2311 are each 2 microfarad condensers, 400 volts.

Potentiometers 19a, 24a, 41 and 45 are each rated at 10 megohms.

Tubes 18a and 43 are 6P5 standard vacuum triodes.

Tubes 34a and 34 are standard type 211 transmitter triodes.

Tubes 35, 35a, 36, 36a, 37, 37a, 38, and 38a are type 816 standard halfwave mercury rectifier tubes.

Conductors 26a, 25a, 30a and 31a and all conductors connecting thecomponent elements are all number 14 gauge insulated wire.

Neon tube 32a may be any gaseous discharge tube of inside diameter of 20millimeters and a gas pressure of about 0.5 millimeter of mercury to 20millimeters of mercury. fl

Transformer 33a is any ordinary neon tube transformer,

17 the one used here has a primary voltage of 110 volts, 60 cycles and asecondary voltage of 2500 volts.

Resistors 49a are all 500 ohm carbon resistors.

Fig. 10

Transformers 11b, 11c, 20b, 200, 425 and 420 each have a primary Winding110 volts, 60 cycles, and a secondary winding 700 voltswith a centertap.

Tubes 12b, 12c, 21b, 210 are standard Y3 rectifier tubes.

Tubes 17b, 17c are 2050 standard thyratron tubes.

Adjustable resistors 13b, 13c, 22b and 22s are 3 megohrn potentiometers.

Condensers 14b, 140, 2315, 230 are each 2 microfarad condensers.

Potentiometers 19b, 19c, 24b, 24c, 41b, 41c, 43b and 450 are all ratedat megohms.

Tubes 18b, 18c,43b,"43c are 6P5 vacuum triodes.

Transformers 32b and 32c are ordinary neon tube transformers, thoseusedhere have a primary voltage of 110 volts at 60 cycles and asecondary voltageof 2500 volts.

Resistors 49b and 49c are 500 ohm carbonresistors.

Tubes 34b and 340 are standard 211 type transmitter triodes.

Tubes 35b, 35c 36!), 36c, 37b, 37c, 38b and 38c are all type 816 'halfwave mercury. rectifier tubes.

Conductors 25b,25c,26b, 26c, 30b, 30c, 31b, 31c, and 60 and allconductors connecting component units or elements are number 14 gaugeinsulated wire conductors, with insulation for 400 volts.

Light tubes 32b and 320 may be any gaseous discharge tubes of insidediameter of 20 millimeters anda gas pressure of about 0.5 i020millimeters of mercury, the difrference between 32b.and 32c being-thecolor of the light producedbythe tubes.

Fig.1]

Transformers "70 and20-each have a primary voltageof 110 volts 60cycles, and a-secondary voltage of 700 volts and a secondary center tap.

Tubes 72 and 121 are each type5Y3 rectifier 'tubes.

Tube 76 is a standard 2050'thyratron;

Adjustable resistors 74 and .18 are 'each 3 megohm standardpotentiometers.

Condensers and .23 are 2 microgaradcondensers.

Potentiometers 19"and1 2141are'eachratedat l0 megohms.

Resistors 49N'and49M are. 1000 ohm carbonresistors.

Conductors 25 and26 andall conductors connecting component unitsorelements are 14 :gaugewire conductors with insulationl for 400 volts.

The units or elements in general have thesame values and identities asset forth for the corresponding parts illustrated in Fig. 9. Impedances90 and '91 :were of same valueand such irnpedance Wassupplied by neontube 32a forelement 01. Impedance 9t may be a similar and equal load(not necessarily, however, equal) and provided by a neon tube.Impedancein-thisFig. 12 may be any impedance as-thoseinvolved inapplying the circuits of my invention and discovery inexperimentation asstated. As willbe understood by those skilled in the art, the range ofvalue for such impedances may vary widely.

If desired'to increase the time cycle fromone minute to two minutes,then one would approximately. doublewthe resistance of the adjustableresistors, or leavetheresistors unchanged and double the capacitancerating of the condensers employed that is, for a, general ruleprovideresistor-condenser combinations which have a R.-C. timeconstantproportional to the desired increasein the, length of the timecycle.

Specific values, ratings. andcharacter of .meanshave been given by way.of illustration, not limitation. They do disclose a general relationshipand teach those skilled in the art how to adapt the invention anddiscovery to specific applications. The invention and discovery is not18 adapted to be defined by any all inclusive formula for values,ratings and means in all cases. But the relationship is set forth, sothat those skilled in the art may readily know how to apply theinvention and discovery.

I claim:

1. A low-frequency signal generator comprising a re.- laxationoscillatorof the grid-controlled thyratron type having in the blocking circuitthereof a time constant network and having in the output circuit thereofa time constant network intermittently charged from a direct currentsource, said low-frequency signal generator further comprising means forselecting; at least a portion of thesignal developed across thesecond-mentioned time constant network and impressing the same on thegrid of a grid-controlled vacuum tube having in the plate. circuitthereof a time constant network intermittently charged from a seconddirect current source, and means for, se

lecting at least a portion of the signal generated across saidlast-mentioned time constant network as the output low-frequency signal.

2. A low-frequency signal generator capable of wide variation in. output.waveform, comprising a relaxation oscillator of the. grid-controlledthyratron type having in the blocking circuit thereof a variable timeconstant network ,andhaving in the output circuit thereof a secondvariable time constant network intermittently charged through arectifier, said. low-frequency signal generator further comprisingvariable means forselecting at .least a portion of the signal developedacross said second time constant network and impressing the sameon thegrid ofa grid-controlled vacuum tube having in the plate circuit thereofa variable time constant networkrintermittently charged through asecondrectifier, and variable means for selecting at least a portionof thesignal generated across said last-mentioned time constant network astheoutput low-frequency signal.

3. A low-frequency signal generatorcapable ofwide variation in outputsignal waveform, comprising a relaxation oscillator of thegrid-controlled thyratron type havingin the blocking circuit thereof'afirst variable means including a time constant network .for adjustingthe repetition rate of the output signal, saidv thyratronhaving in theplate circuit thereof a, second variable means includinga time constantnetwork intermittently charged throughea rectifier circuit under controlof said thyratron, said second variabledmeansadjusting the rate ofvoltageincrease of said, output signal, ,said low-frequencysignalgenerator further comprising ,a third .variable means .forselecting at least .a portion of thesignal developedacross saidsecond-mentioned time constant network .to selectively adjust the shapeof saidoutput signal at the maximum and minimurnvoltage portionsthereof, such selected signal .beingimpressed upon .the grid of agrid-controlled amplifier having in the plate circuitthereof a fourthvariable means including a time constant network intermittentlychargedthrough, a second rectifier circuit under control of saidamplifier, said fourth variable means adjusting the rate. of voltagedecrease of said output signal, and a fifth variablemeans for selectingat least a portion of the signal generated' across said last-mentionedtime constant network to determine the amplitude of said output signal.

4. An illumination display system comprising a gaseous displaytube,..-means for supplying a high-voltage alternating current to saiddisplay tube, variable impedancemeans in circuit with said gaseousdisplay tube, and a low-frequency control signal, generator for varyingthe: impedance of said variable impedance means said low-frequencysignal generator comprising a relaxation oscillator of thegrid-controlled thyratron type having in the blocking circuit'thereof atime constant network and having in the output circuit thereof a timeconstant network intermittently charged through a rectifier circuit,said low-frequency control signalgeneratorfurther comprising means forselecting at least a portion of the signal developed across thesecond-mentioned time constant network and impressing the same on thegrid of a grid-controlled vacuum tube having in the plate circuitthereof a time constant network intermittently charged through a secondrectifier, and means for selecting at least a portion of the signalgenerated across said last-mentioned time constant network to controlthe impedance of said variable impedance means.

5. An illumination system according to claim 4 wherein said relaxationoscillator is free-running.

6. An illumination system according to claim 4 wherein at least aportion of the output of said low-frequency signal generator isimpressed on means developing a trigger pulse in turn connected by feedback means to the grid of said relaxation oscillator to preciselymaintain the repetition rate of the low-frequency control signalgenerator.

7. An illumination system according to claim 4 wherein said variableimpedance means comprises a bridge rectifier network with thealternating current terminals thereof connected in series with saiddisplay tube, said bridge rectifier network also including agrid-controlled vacuum tube having the plate and cathode thereofrespectively connected to the positive and negative direct currentterminals of said bridge rectifier network, the selected output of thethe low-frequency control signal generator being impressed on thecontrol grid of said latter-mentioned vacuum tube.

8. An illumination display system comprising a gaseous display tube,means for supplying a high-voltage alternating current across saiddisplay tube, variable impedance means in series with said gaseousdisplay tube, and a low-frequency control signal generator for varyingthe impedance of said variable impedance means to cause cyclic variationin the illumination intensity of said gaseous display tube, saidlow-frequency control signal generator comprising a relaxationoscillator of the gridcontrolled thyratron type having in the blockingcircuit of said thyratron a variable time constant network and having inthe plate circuit of said grid-controlled thyratron a variable timeconstant network intermittently charged through a rectifier, saidlow-frequency signal generator further comprising variable means forselecting at least a portion of the signal developed across thesecond-mentioned time constant and impressing the same on the grid of agrid-controlled vacuum tube having in the plate circuit thereof avariable time constant network intermittently charged through a secondrectifier, and variable means for selecting at least a portion of thesignal generated across said last-mentioned time constant network tocontrol the impedance of said variable impedance means, causingcorresponding variation in the illumination intensity of said displaytube.

9. An illumination display system comprising a gaseous display tube,means for supplying a high-voltage alternating current across said tube,variable impedance means in circuit with said gaseous display tube tocause variation in the illumination intensity thereof, and alow-frequency control signal generator for producing a control signal tovary the impedance of said variable impedance means, said generatorcomprising a relaxation oscillator of the grid-controlled thyratron typehaving in the blocking circuit thereof a first variable means includinga time constant network for adjusting the repetition rate of saidcontrol signal, said thyratron having in the plate circuit thereof asecond variable means including a time constant network intermittentlycharged through a rectifier circuit under control of said thyratron,said second variable means adjusting the rate of voltage increase ofsaid control signal, said low-frequency signal generator furthercomprising a third variable means for selecting at least a. portion ofthe signal developed across said second-mentioned time constant networkto selectively adjust the shape of said control signal at the maximumand minimum voltage portions thereof, such selected signal beingimpressed upon the grid of a grid-controlled amplifier having in theplate circuit thereof a fourth variable means including a time constantnetwork intermittently charged through a second rectifier circuit undercontrol of said amplifier, said fourth variable means adjusting the rateof voltage decrease of said control signal, and a fifth variable meansfor selecting at least a portion of the signal generated across saidlast-mentioned time constant network to determine the amplitude of saidcontrol signal.

10. A system according to claim 9 wherein said relaxation oscillator isfree-running.

11. An illumination system according to claim 9 wherein at least aportion of the output of said lowfrequency control signal generator isinverted in phase to provide a trigger pulse, and means for impressingsaid trigger pulse on the blocking circuit of said relaxation oscillatorto precisely maintain the repetition rate of said low-frequency controlsignal generator.

12. An illumination system according to claim 9 wherein said variableimpedance means comprises a bridge rectifier network with thealternating current terminals thereof connected in series with saiddisplay tube, said bridge rectifier network also including agrid-controlled vacuum tube having the plate and cathode thereofrespectively connected to the positive and negative direct currentterminals of said bridge rectifier network, the selected output of thelow-frequency control signal generator being impressed on the controlgrid of said lattermentioned vacuum tube.

13. An illumination control system comprising a plurality of gaseousdisplay tubes; means for supplying a high-voltage alternating current toeach of said display tubes; and a plurality of illumination intensitycontrol means, one in circuit with each of said display tubes, each suchcontrol means comprising a variable impedance means controlled by alow-frequency control signal generator including a relaxationoscillator, each said illumination intensity control means furthercomprising means for impressing at least a portion of the low-frequencycontrol signal produced by each said generator on the associatedvariable impedance means to cyclically vary the impedance thereof; and are-cycling circuit for developing a trigger signal from the output ofone of said control signal generators and delivering such trigger signalto the relaxation oscillator circuit of a second of the said generatorsto provide synchronization therebetween and produce cyclically relatedvariation in the illumination intensity of said display tubes.

14. An illumination control system comprising a plurality of gaseousdisplay tubes; means for supplying a high-voltage alternating current toeach of said display tubes; and illumination intensity control meansassociated with each of said display tubes, each such intensity controlmeans comprising a bridge rectifier network with the alternating currentterminals thereof connected in series with an associated display tube,said bridge rectifier network also including a grid-controlled vacuumtube having the plate and cathode thereof connected to the directcurrent terminals of said bridge rectifier network, each saidillumination intensity control means further comprising a low-frequencycontrol signal generator in cluding a relaxation oscillator, each saidillumination intensity control means further comprising means forimpressing at least a portion of the low-frequency control signalproduced by said generator on the grid of the associated grid-controlledvacuum tube to cyclically vary the impedance of the associated rectifiernetwork; and a recycling circuit for developing a trigger signal fromthe output of one of said control signal generators and delivering suchtrigger signal to the relaxation oscillator circuit of a second of saidgenerators to provide synchronization therebetween and producecyclically related 21 variation in the illumination intensity of saiddisplay tubes.

15. An illumination control system comprising a plurality of gaseousdisplay tubes; means for supplying a high-voltage alternating current toeach of said display tubes; illumination intensity control meansassociated with each of said display tubes, each such control meanscomprising a variable impedance means, each said illumination intensitycontrol means further comprising a low-frequency control signalgenerator including a variable frequency relaxation oscillator of thegrid-controlled thyratron type; and means for impressing at least aportion of the low-frequency control signal produced by said generatoron the control circuit of said variable impedance means to cyclicallyvary the impedance thereof; and a synchronization circuit includingmeans for generating a trigger signal from the low-frequency controlsignal produced in one of said generators and means for delivering saidtrigger signal to the relaxation oscillator thyratron blocking circuitof a second of said generators to provide synchronization therebetweenand produce cyclically related variation in the illumination intensityof said display tubes.

16. An illumination control system according to claim 15 wherein saidsynchronization circuit further includes means for generating a secondtrigger signal from the low-frequency control signal produced by saidsecond generator and means for delivering said second trigger signal tothe relaxation oscillator thyratron grid of said first low-frequencycontrol signal generator.

17. An illumination control system according to claim 16 wherein saidfirst and second trigger signals are related in phase to cause inversevariation in the illumination intensity of said display tubes.

References Cited in the file of this patent UNITED STATES PATENTS1,898,827 Franklin Feb. 21, 1933 1,926,181 Schramm Sept. 12, 19332,005,893 Gulliksen June 25, 1935 2,008,494 Elder et al. July 16, 19352,275,308 Niemann Mar. 3, 1942 2,457,176 Preisman Dec. 28, 19462,522,492 Anderson Sept. 19, 1950 2,760,069 Cole Aug. 21, 1956

